1. Field of the Invention
The present invention relates to a structure for mounting a substrate carrying a superconducting circuit such as a superconducting filter circuit thereon.
2. Description of Related Art
An example of a conventional mounting structure of a superconducting filter circuit is shown in FIG. 11. A filter substrate 101 made of a dielectric material carries a resonator pattern 102 made of a superconductor and formed on its upper surface and a ground plane 103 also made of a superconductor and formed on its lower surface. A gold film electrode 104 is formed on the ground plane 103. The filter substrate 101 is fixed on a base plate 106 made of copper by conductive paste 105 and covered by a cover 107 made of aluminum. Thus, a filter 100 is constituted.
When the filter 100 is operated, a cold head 109 is attached to the filter 100 via a heat dissipation plate 108, and the filter 100 is contained in a container 110 which is kept at a low temperature under vacuum. The filter substrate 101 is cooled down by the cold head 109 and kept at a cryogenic temperature. The cold head 109 is made of a material having a low heat conductivity and a high mechanical strength, such as titanium or stainless steel. The cold head 109 is a cylinder having a very thin thickness, and helium gas of about 20 atm is filled in the cylinder. The cylinder thickness is several tens micrometers, which is the minimum to endure the pressure of helium gas. Input/output terminals (not shown) of the superconducting filter are connected to a connector mounted on the base plate 106. The connector on the base plate 106 is further connected to another connector mounted on the container 110 through a coaxial cable, thereby making an electric connection between the superconducting filter and an outside circuit.
In case a multi-channel circuit having several filters 100 is required, the several filters 100 are contained in a single low temperature container 110 as shown in FIG. 12. Each filter 100 is disposed in the container 110 and connected to the cold head 109 through a heat conductive member 111. In this structure, since the cold head 109 has to carry plural heat conductive members 111 thereon, the weight thereof imposes a heavy load on the cold head. Moreover, a large refrigerator having a high capacity is required in this structure.